Recently, a high-intensity discharge lamp provided with a light-transmissive ceramic enclosure which is more profitable in its life-expectancy and lighting efficiency than a conventional discharge lamp silica glass enclosure.
FIG. 30 is a partial enlarged front section showing a sealing portion of a high-discharge lamp provided with a conventional light-transmissive ceramic enclosure.
FIG. 31 is another partial enlarged front section showing a sealing portion of a conventional high-discharge lamp.
In FIGS. 30 and 31, the numeral 101 denotes a small diameter cylinder portion. Also, the numeral 102 denotes a feed-conductor, and the numeral 103 denotes a sealant.
The small diameter cylinder portion 101 is coupled to one end of an envelope (not shown) defined in the center of a discharge lamp light-transmissive ceramic enclosure. While the small diameter cylinder portions 101 is defined a through-holes 101a which communicates to the envelope.
The feed-conductor 102 is provided with a sealable portion 102a and a refractory portion 102b.
The sealable portion 102a is comprised of a sealable portion 102a1 which may be inserted in the small diameter cylinder portion 101, and an outer protrusion 102a2 having a tip end to be coupled to the base end of the sealable portion 102a1 and a base end protruding outside the small diameter cylinder portion 101.
The base end of the refractory portion 102b is coupled to the tip end of the sealable portion 102a made of the sealable metal. Further an electrode is mounted on the tip end of the refractory portion 102b (not shown). In order to couple the base end of the refractory portion 102b to the tip end of the sealable portion 102a, steps 102a3 and 102b1 are placed on, e.g., the tip end of the sealable portion 102a and the base end of the refractory portion 102b at their positions to be welded each other. The steps 102a3 and 102b1 are superimposed and then spot-welded each other up and down.
Further, the feed-conductor 102 is inserted into the small diameter cylinder portion 101. Then a compound of a sealant 103 for sealing ceramics flows into the narrow gap between the small diameter cylinder portion 101 and a sealing portion 101a1 of the sealable portion 102a of the feed-conductor 102 inserted in the small diameter cylinder portion 101 and then solidified so that the small diameter cylinder portion 101 is sealed and the feed-conductor 102 is fixed to a predetermined position,
By the way, the outer protrusion 102a2 of the sealable portion 102a of the feed-conductor 102 protrudes outside and its tip end is coupled to the bane end of the sealable portion 102a1. In a type of a outer bulb being housed in an exhausted outer bulb and lighting therein, the outer protrusion 102a may protrude outside the discharge lamp light-transmissive ceramic enclosure 101 and effect as an external lead-wire. However, in a type of a outer bulb exposing in air, the outer protrusion 102a must be sealed hermetically by the sealant so as not to be exposed in air for preventing from oxidation.
Accordingly, in the type of the outer bulb exposing in air, the outer protrusion 102a2 is coupled to an external lead-wire (now shown) made of an oxidation-resistant metal, and the junction is fit around by the ceramic washer (not shown), and sealed by a sealant with a melting point lower than that of the sealant 103.
Further, for coupling the tip end of the outer protrusion 102a2 to the base end of the sealable portion 102a1, steps 102a4 and 102a5 defined in the sealable portion 102a1 and the outer protrusion 102a2 are superimposed each other and then spot-welded.
To solve the problems in the prior art discharge lamp as described above, the inventors have developed a new high-intensity discharge lamp in which the sealable portion of the feed-conductor is formed by rounding a plate in a cylindrical shape with a junction line and filed the invention (hereinafter referred to prior invention) in Japan (Japanese Patent Application 10-257807). Accordingly the sealable portion becomes easy to be coupled to a refractory portion whose tip end being provided with an electrode. The sealable portion then becomes hard to be off-centered from the refractory portion.
FIG. 32 is a partial enlarged front section showing the prior invention of the high-intensity discharge lamp.
In FIG. 32, the same elements as those shown in FIG. 31 are assigned with same marks.
The sealable portion 102a of the feed-conductor 102 is comprised of a cylindrical sealable portion 102a1' and an outer protrusion 102a2.
The cylindrical sealable portion 102a1' is formed by cylindrically rounding a sealable metal plate. Thus the cylindrical sealable portion 102a1' has an axially extending junction line j which presents a narrow gap of about 1 to 10 .mu.m in average.
The outer protrusion 102a2 is inserted into the cylindrical sealable portion 102a1'. They are thus possible to be coupled each other by a shrinkage fitting at the sealing operation.
The refractory portion 102b is inserted into the cylindrical sealable portion 102a1', and then coupled thereto by a shrinkage fitting in the same way as that of the outer protrusion 102a2.
By the way, the conventional arts have same drawbacks at the junction of the sealable portion and the refractory portion in the feed-conductor, and at the junction of a sealing and the outer protrusion in the sealable portion. That is, there are problems of that such a spot welding is troublesome and that those thus spot-welded are easy to be off. centered from each other.
The prior-art high-intensity discharge lamp is favorable in that it is easy to couple the sealable portion and the refractory portion and they are hardly off-centered from each other. However, when taken a configuration that the sealant fails to enter inside the cylindrical sealable portion 102a1', if it Leaks of the sealant occur at both the junction of the refractory portion and the cylindrical sealable portion 102a1' and the junction of the cylindrical sealable portion 102a1' and the outer protrusion 102a2, the discharge lamp light-transmissive ceramic enclosure 101 looses a hermeticity. However, such a problem could be solved in easy according to the present invention.